This invention relates to imaging devices. More particularly, this invention relates to the placement of transitions in a data stream in an imaging device.
In an imaging device, such as an electrophotographic printer, copier, or fax machine, that uses a scanning device to expose a photoconductor, imaging data is used to control the application of current to a laser diode to form a latent electrostatic image on the surface of the photoconductor. The laser diode generates a beam that is swept across the surface of the photoconductor by the scanning device. The generation of high quality images can be accomplished by precisely controlling exposure of the photoconductor. The image is quantized into pixels that have a dimension in the direction the beam moves across the surface of the photoconductor. An improvement in image quality can be accomplished by decreasing the minimum quantization size of the area developed onto the photoconductor for the dimension of the developed area in the direction the beam is swept across the surface of the photoconductor. In addition to decreasing the minimum quantization size of the area developed, improved image quality is also accomplished by precisely controlling the positioning of the developed area with respect to the direction the beam is swept across the surface of the photoconductor. Decreasing the minimum quantization size can be accomplished by decreasing the minimum time period that the laser diode can be turned on during a sweep across the surface of the photoconductor. A need exists for a method and apparatus that will permit a decrease in the minimum laser on time period while precisely positioning the corresponding developed area on the surface of the photoconductor.
Accordingly, a method for generating a first transition of a first signal, used to control a light source in an imaging device, within a first time interval has been developed. The method includes determining a second time interval beginning with a second transition of a second signal and ending with detecting a third signal changing out of a first state. The method further includes shifting a predetermined position in time of the first transition with respect to a third transition of the second signal by the second time interval to determine a position in time of the first transition. In addition, the method includes generating the first transition of the first signal at the position.
In an electrophotographic imaging device, a transition placement device to generate a first transition of a first signal, used to control a light source, in a first time interval using a first value, includes a phase measuring device configured to determine a second value using a second time interval beginning with a second transition of a second signal and ending with detection of a change of a third signal out of a first state. The transition placement device further includes a transition adjustment device configured to determine a third value, representing a position in time of the first transition relative to a third transition of the second signal, using the first value and the second value. In addition, the transition placement device includes a transition generation logic configured to generate the first transition at the position using the third value.
An electrophotographic imaging device for forming an image using data includes a photoconductor and a rasterizer configured to generate pixel data corresponding to a pixel time period using the data. The electrophotographic imaging device further includes a circuit configured to generate a position in time of a first transition of a video data signal relative to a second transition of a reference clock using the pixel data. In addition, the electrophotographic imaging device includes a transition placement device. The transition placement device includes a phase measuring device configured to determine a first time interval between a third transition of the reference clock and a state change of a beam detect signal. Additionally, the transition placement device includes a transition adjustment device configured to generate an adjusted position in time relative to the second transition of the reference clock using the first time interval and the position. The transition placement device also includes transition generation logic configured to generate the first transition in the pixel time period using the adjusted transition position. The electrophotographic imaging device further includes a photoconductor exposure system configured to expose the photoconductor to light according to the first transition.
In an imaging device, a method for adjusting a position in time of a transition of a signal relative to a reference clock includes measuring a first time interval between a first rising edge of the reference clock and a change in state of a phase reference signal. The method further includes shifting the position of the transition relative to a second rising edge of the reference clock by the first time interval forming an adjusted position in time. Additionally, the method includes generating the transition at the adjusted position.